The realization of subsea oil and gas processing call for new technologies within electrical power systems and components. There is currently a need for local supply systems close to wellheads serving equipment such as gas boosters, oil pumps and separators. In the future we anticipate the development of supply systems for long step-outs where high voltage DC represents a viable solution. Due to the very high reliability and operability demands for subsea processing equipment there will also be a very high reliability and ruggedness demands for electric components and system solutions.
Large power converters like for gas boosting are assumed to be located on the seabed at various depths, possibly in excess of 3000 metres. Current designs offered by the industry for subsea converter operations are based on concepts in which the power circuits are assembled in their entirety in steel vessels at atmospheric pressure. As operational water depths and converter power rating increase, pressure vessels become increasingly heavy and unwieldy due to the need to increase wall thickness. Consequently, heat transfer from the power electronics components to the seawater becomes problematic. For this reason, the oil companies are looking for less cumbersome subsea power electronics systems. The development of pressure tolerant power circuits is a significant step in the right direction, opening the door to reducing device weight and volume. Furthermore, systems such as this will provide opportunities for improved power component cooling systems that will increase reliability and reduce costs. The availability of reliable pressure tolerant converter systems will enable the introduction of new concepts for subsea transmission and electrical power distribution, including the use of DC and frequencies other than the 50/60Hz range. Indeed such enabling technologies will also open up for quite new concepts for electric power transmission and distribution within the renewable energy sector such as for offshore wind power.
In the previous research project on pressure tolerant power electronics 2006-2012, Feasible power electronics for demanding subsea applications, the operability of live switching converter modules was clearly demonstrated. However, the voltage range for the test objects was limited to 1000 V. It was also recognized that in order to achieve pressure tolerant products with the sufficient long-term reliability, some remaining fundamental problems had to be solved. The problems and uncertainties were mainly related to materials for electric insulation, and how to apply the materials for appropriate packaging of the most vulnerable components. Higher voltage and power ratings and problems related to electrical insulation have been the main focused topics in PressPack.
Ref also: Under Pressure - a popular science article in the magazine international innovation, issue June 2013